This disclosure is directed to polysiloxane-polycarbonate compositions, and related methods and articles.
Polysiloxane-polycarbonates comprising aromatic carbonate units and polysiloxane carbonate units typically exhibit phase separation, as evidenced by low transparency and high degrees of haze. These optical characteristics can limit the utility and potential applications of such copolymers. There accordingly remains a need for compositions comprising polysiloxane-polycarbonates characterized by high transparency and low haze, in combination with other desirable properties such as melt flow, low temperature ductility, flame retardance (FR), and retention of mechanical properties such as impact strength after accelerated aging at elevated temperature and humidity (hydro-aging). Impact strength can be significantly degraded under such conditions within a few days.
A variety of flame retardant additives have been used in the past for obtaining low flammability at low thicknesses in various polymers. U.S. Pat. No. 4,816,527 discloses improved impact strength, enhanced physical properties and low flammability in polycarbonate and polysiloxane-polyetherimide blends. Also, US Patent Application 2007/0048527A1 discloses flame retardant polymer blends containing polycarbonate, polysiloxane-polycarbonate copolymer, and polyetherimide. However, in each of the above-mentioned prior art references, good FR performance is achieved only for opaque materials. Opaque polysiloxane-polycarbonates comprising flame retardant additives such as Rimar salt are available and have achieved a UL94 (Underwriter's Laboratory) flammability rating of V0 at thicknesses as low as 1.5 mm. Clear polysiloxane-polycarbonates, by comparison, remain a challenge with respect to achieving good flame retardance at low thicknesses, and retaining optical transparency.
Accordingly, a need exists for transparent polysiloxane-polycarbonates having good retention of mechanical properties after hydro-aging, and excellent flame retardant properties, in combination with other desirable properties such as melt flow and/or low temperature ductility.